Field of the Invention
Embodiments of the present invention relate to a rotor for an electric motor, an electric supercharger, and an electric-motor assisted supercharger. More particularly, embodiments of the present invention relate to a rotor for an electric motor, an electric supercharger and an electric-motor assisted supercharger that are suitable for use as vehicle-mounted equipment.
Background Art
An electric-motor assisted supercharger to be mounted in a vehicle is disclosed in Japanese Patent Laid-Open No. 2007-321675. The electric-motor assisted supercharger includes a shaft that extends from a turbine side to a compressor side. A rotor sub-assembly is mounted on the shaft so as to be positioned between the turbine and the compressor.
The rotor sub-assembly includes a ring-shaped magnet. The magnet is press-fitted into the inside of a ring-shaped member. End-plates are press-fitted into the two ends of the ring-shaped member so as to come in contact with the two ends of the magnet. Spacers are disposed on both a turbine side and a compressor side at positions that are further on the outer side of the end-plates. The spacers are provided so as to sandwich the two sides of the ring-shaped member without contacting the adjacent end-plates.
In the aforementioned Japanese Patent Laid-Open No. 2007-321675, a small-diameter portion that passes through the rotor sub-assembly, and a large-diameter portion that connects to the small-diameter portion are provided in the shaft of the electric-motor assisted supercharger. The position of the rotor sub-assembly on the shaft is determined by one of the spacers contacting against an end portion of the large-diameter portion. The aforementioned position can be maintained by applying compressive stress to the other spacer so that the aforementioned one of the spacers does not separate from the end portion of the large-diameter portion.
In the aforementioned Japanese Patent Laid-Open No. 2007-321675, the compressive stress that is applied to the two spacers acts only on the ring-shaped member, and is not transmitted to either of the end-plates. Consequently, according to this configuration, the rotor sub-assembly can be maintained at an appropriate position on the shaft without applying excessive compressive stress to the magnet.